Various methods of heat treating metal substrates are known and include heating a metal substrate to an elevated temperature and then cooling. The cooling step, which is known in the art as “quenching”, typically is performed rapidly and is accomplished by either immersion quenching or spray quenching Immersion quenching involves immersing the hot metal substrate in a liquid quenching medium, i.e. a quenching bath. Spray quenching involves spraying quenchant on the heated metal part as it travels through a quench barrel or quench ring. The process of quenching involves the use of certain hydraulic equipment, which requires hydraulic fluids for performance. These quenching systems typically use large amounts of both aqueous quenchant and hydraulic fluid. The amount of quenchant used can be sizable depending upon the size of the metal product that is being quenched.
A metal quenchant, e.g., bath or spray, is typically made up of a variety of known quenching products (polymer and additives) and water. To cool the metal appropriately, a functional quenchant must meet selected quenching specifications, which can be unique to each quenching product. These quenching specifications are monitored during the quenching process. If or when the quenching specifications are no longer met by the bath or spray during the quenching process, the quenching bath or spray becomes ineffective and results in unsatisfactory (i.e., delayed) cooling of the metal or an unsatisfactory (e.g., warped, marked or cracked or otherwise deformed) metal substrate produced from the quenching process.
While components of the aqueous quenching bath or spray can become too concentrated due to heat and/or the quantities of materials in the bath or spray can reach unusable ratios, it is generally contamination with the hydraulic fluid from the hydraulic equipment which causes the quenchant to cease to meet its quenching specifications. Therefore, periodically, the quenchant components in the bath or spray must be replenished.
Commonly, a quenching process employs an aqueous quenching product and the hydraulic equipment employs a water glycol-based hydraulic fluid, e.g., such as those represented by the trade names, Houghto-Safe® 419R and Houghto-Safe® 620 hydraulic fluid (Houghton International, Inc.) In such systems the aqueous quenchant in the quenching bath or spray becomes contaminated by the water glycol hydraulic fluid. The resulting contaminated quenchant is a fluid from which the two components cannot be readily separated for recovery and reuse. The entire contaminated quenchant removed from the quenching bath tank or spraying devices is directed to waste streams when the quenching bath or spray fails to meet its quenching specifications. There is no useful recycling due to the miscibility of the two major components. Waste treatment typically entails mixing the waste with water, thereby generating in excess of 100,000 gallons of waste water per day for the metal quenching industry.